Modern camera designs often include automatic functions needed to produce technically correct photographs, transport film forward or in reverse as needed, determine film speeds, adjust electronic flash power and duration, and other functions. However, photographers using color film find that the color temperature of light illuminating their subjects, also called incident light, rarely corresponds to the color temperature standard to which the film was manufactured. Daylight type color film requires a blue filter to compensate for excessively yellow incident light, whereas a yellow filter is needed to compensate for excessively blue incident light. To achieve a balance between the color temperatures of the incident light and the film's color temperature standard, a photographer must either guess or measure the color temperature of the incident light and install over the front of the lens one of a few available choices of color correcting filters.
In the science of color measurement and manipulation measurement of the intensity, purity, or saturation, all of which are synonomous terms, of the red and blue components of incident light effectively allows correct reproduction color on film. Red, blue, and yellow are spoken of as primary colors but manipulation or changing purity of yellow and blue colors is sufficient for our purpose even though the colors of the rainbow which result from separation of sunlight are usually spoken of as violet, indigo, blue, green, yellow, orange and red.
Recently dyed and undyed dichroic liquid crystal filters, available from Crystalloid Electronics Co. in Hudson, Ohio, Hamlin, Inc. in Lake Mills, Wis. and others, may be used to effectively change the color temperature of light going through a filter. The output from these filters may be varied by impressing an alternating current to vary their purity, hence, the transparency and the amount of yellow or blue light emitted by the filter. A combination of a variable yellow filter and a variable blue filter allows correction of incident light to match the color temperature standard to which the film is manufactured.
The color temperature standard to which daylight film is manufactured is approximately 5,400 degrees K which is the yearly average of the color temperature of sunlight measured daily at noon in Washington, D.C. Color films for making photographs of subjects illuminated with incandescent lamps are designed to produce proper colors when the incandescent lighting is approximately 3,200 degrees K. Films designed to balance colors under other color temperature conditions are also available.
This invention includes components as follows that may be either installed into the body of a camera or into a front-of-the-lens device which is designed for independent operation and attachment to the camera:
1) A manual switch to set the device to either off, or automatic or manual mode of operation. PA1 2) Two photosensors, one each for detecting and producing electrical outputs corresponding to the red and blue components of incident light illuminating the photographic subject. PA1 3) An electronic central processing unit to receive information and data inputs from the various peripheral switches and sensors; calculate the currents needed for proper operation of the variable color filters; control the supply of electrical currents to the variable color filters; and, output data to other optionally installed devices. PA1 4) A device built into the camera for the purpose of reading a color standard code imprinted or otherwise installed on the film by the film manufacturer and transmitting this information to the central processing unit for use in computing the proper color filter adjustments. PA1 5) DC power supply which may be a battery installed in the camera or in the front-of-the-lens device. PA1 6) A variable color correction filter unit which is designed for installation inside the camera body at a position between the camera lens and film, or for attachment to the front of the camera lens. PA1 7) An optional manual control to vary the color purity of each element of the filter. This feature will permit the photographer to increase or decrease either the yellow or blue color of photographs. PA1 8) An optional switch to lock the photo sensitive device measurement of incident light into the computational circuitry of the central processor unit. This will permit photographers to take close-up measurements of the predominant color of incident light illuminating the photographic subject, move some distance away from the subject without the device automatically correcting for other colors of incident light that may be prevalent, and correct or enhance the photograph according to the desires of the photographer. PA1 9) An optional electronic display such as light emitting diodes or a liquid crystal display to indicate color temperature of incident light illuminating the subject as well as corrected color temperatures of light after passing through the variable color filter may also be included. PA1 a) An electric color balance switch to set the mode to either "Automatic," "Manual," or "Off" to allow the user to choose use of automatic operation for normal color balance or manual color change for special effects. PA1 b) A Color Balance Lock, which is an electrical switch, manually operated to lock into the CPU the color temperature measurement of light illuminating a portion of photographic subject, such measurement to be used for subsequent use when taking a photograph. PA1 c) A Filter Color Purity Control, which comprises an electrical switch, manually operated, to adjust the color purity of either the blue or yellow filter element, thus permitting the photographer to employ, at will, a blue or yellow cast to photographs for artistic or other desired effect. PA1 d) A means to enter the color film type into the CPU which may be an automatic detector or manually operated switch to set the color temperature rating of the film being used in the camera. PA1 e) A sensor device installed to detect and output electrical current to a central processing unit based on measurement of the red and blue components of incident light. PA1 f) A liquid crystal device to display the color temperature of the visible light illuminating a photographic subject and optionally, the color temperature of light after passing through the color filter device.
Alternatively, a manual switch for selecting the color rating of the color film inside the camera, i.e., daylight type film, indoor type film, or other color standard may be used. A central processor, CPU, takes into account such settings when computing the proper filter adjustments to balance the color temperature of incident light with the film type.
This variable color correction filter unit has two separate layers: a first layer of reverse mode dichroic liquid crystals that is normally essentially transparent but that becomes increasingly more yellow as an alternating current is impressed across the layer and a second layer of reverse mode liquid crystals that becomes increasingly more blue as an alternating current is impressed across the layer. Regular mode liquid crystal filters achieves the same results, but the color purity with no electrical current applied is dark and becomes transparent in relationship to the amount of alternating current applied.
Although this invention is described in terms and details to completely automate a camera, many other uses are visualized including, but not limited to, color variation and enhancement by polarization or other means for use with microscopes, color measurement, and automating control systems dependent upon color. We, therefore, wish to be limited only to spirit and purpose as outlined in these claims and specifications rather than specific details.